1. Field of the Invention
This invention relates to a device and a method to ensure the steerability of an industrial truck that has a hydraulic steering system and, in one embodiment, to an emergency steering device for an industrial truck.
2. Technical Considerations
Hydraulic steering systems are the standard steering systems on industrial trucks that have a driver's seat. With this type of steering system, the steering force exerted by the driver (if the vehicle is equipped with a mechanical steering system) is hydraulically assisted. A hydraulic pump is driven by the motor of the industrial truck. The steering force is amplified by the pressure that is exerted on the steering cylinder by the hydraulic medium. In a fully hydraulic steering system, the vehicle can only be steered when the motor is running. A hydraulic steering system can also be electrically assisted (i.e., electro-hydraulic steering).
The prior art discloses hydraulic or electro-hydraulic steering systems that have a second steering pump as a redundant component that can be used if the primary steering pump fails. The purpose of such an arrangement is to guarantee that the industrial truck can be steered or at least be brought into a safe position even after the failure of the first steering pump. Equipping the vehicle with redundant components entails high costs.
The prior art also discloses a hydraulic steering system that has a pressure reservoir instead of the second steering pump. The hydraulic reservoirs of the prior art transmit energy to the hydraulic medium as needed. This method of supplying energy also makes it possible to bring the industrial truck into a secure position in which a repair can then be performed, for example. Normally, the pressure reservoir used has a gas cushion under pressure on one side, a membrane in the middle, and the hydraulic medium on the other side. These systems have a limited useful life on account of the changing pressure load exerted on the membrane. For this reason, the systems of the prior art are maintenance-intensive and expensive.
Therefore, it is an object of the invention to ensure the steerability of an industrial truck in a simple and economical manner, at least for the length of time that is necessary to bring the industrial truck into a safe position.